STABILITY-INDICATING METHODS FOR DETERMINATION OF MELOXICAM AND TENOXICAM IN THE PRESENCE OF THEIR DEGRADATION PRODUCTS

Abstract

ABSTRACT A spectrophotometric and a spectrofluorimetric methods are developed for the determination of two nonsteroidal anti-inflammatory drugs meloxicam I and tenoxicam II in the presence of their degradation products, namely 5-methyl-2-aminothiazole (III), benzothiazine carboxylic acid (IV), for meloxicam, pyridine-2-amine (V) and methyl 4-hydroxy-2-methyl-2H-thienol[2,3-e]1,2-thiazine-3-carboxylate-1, 1-dioxide (VI) for tenoxicam, Fig. 1. Figure 1. The structure of the studied drugs and their degradation products. Both methods are based on the oxidative coupling reaction of these drugs with 3-methylbenzothiazolinone hydrazone (MBTH) hydrochloride in presence of ceric ammonium sulphate in an acid medium. Spectrophotometrically, the resulting stable coloured products showed absorption λ max at 450 nm and 465 nm for meloxicam and tenoxicam respectively. The method was applicable over the concentration range of (2–20 µg mL−1) with mean recoveries 99.90±0.85 and 100.27±1.27 respectively. The method is proved to be stability indicating method, as no reaction was observed with the degradation products. Job plots of absorbance versus mole fraction of drug indicate a 1:1 ratio for both drugs. The variables have been optimized. On the same principle a fluorescence quenching method for the determination of meloxicam and tenoxicam in the presence of their degradation products was developed. The λ ex was 300 nm while the fluorescence intensity was measured at λ em 360 nm. This method is applicable over the concentration ranges (1–10 µg mL−1) for both drugs with mean accuracies 99.88± 0.49 and 99.90±1.02 respectively. The proposed methods were successfully applied for the determination of the studied drugs in bulk powder, laboratory prepared mixtures containing different percentages of degradation products and pharmaceutical dosage forms. The results of the analysis were found to agree statistically with those obtained with either the reported or the official methods. Furthermore the methods were validated and also assessed by applying the standard addition technique.